System and method for managing heat recovery steam generator inlet temperature

ABSTRACT

A system may include a gas turbine system. The gas turbine system may include a compressor, such that the gas turbine system may produce exhaust gas in an exhaust outlet when generating electricity. The system may also include a heat recovery steam generator (HRSG) that may use the exhaust gas to create steam, a manifold system configured to couple compressed air in the compressor to the exhaust outlet, and a controller configured to send a command to the manifold system to couple the compressed air to the exhaust outlet when a temperature of the exhaust gas is above a threshold.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to operating heat exchangers, and more specifically, to systems and methods for managing temperatures within a heat recovery steam generator.

Heat exchangers are used to transfer heat from one medium to another in a variety of industries. A heat recovery steam generator (HRSG) is an example of a heat exchanger, which may be used in combined cycle power plants and similar plants. An HRSG may use gas turbine engine exhaust to heat a fluid flowing through heat exchangers in the HRSG, for example, to convert water into steam. In some configurations, the fluid may be steam used for high-pressure, intermediate-pressure, and/or low-pressure sections of a steam turbine. Generally, the HSRG may be rated to receive mass flows of gases within a particular range of temperatures. As such, improved systems and methods for managing the temperature within the HRSG are desirable.

BRIEF DESCRIPTION OF THE INVENTION

Certain embodiments commensurate in scope with the originally claimed embodiments are summarized below. These embodiments are not intended to limit the scope of the claims, but rather these embodiments are intended only to provide a brief summary of possible forms of the presently disclosed systems and techniques. Indeed, the presently disclosed systems and techniques may encompass a variety of forms that may be similar to or different from the embodiments set forth below.

In one embodiment, a system may include a gas turbine system. The gas turbine system may include a compressor, such that the gas turbine system may produce exhaust gas in an exhaust outlet when generating electricity. The system may also include a heat recovery steam generator (HRSG) that may use the exhaust gas to create steam, a manifold system configured to couple compressed air in the compressor to the exhaust outlet, and a controller configured to send a command to the manifold system to couple the compressed air to the exhaust outlet when a temperature of the exhaust gas is above a threshold.

A non-transitory machine readable medium may include computer-executable instructions that may cause a processor to monitor a temperature of exhaust gas provided to a heat recovery steam generator (HSRG) via an exhaust outlet. The processor may then send a command to a manifold system when the temperature exceeds a threshold, such that the command may cause the manifold system to couple compressed air to the exhaust outlet.

A manifold system may include one or more valves configured to couple compressed air from a compressor of a gas-turbine system to an exhaust outlet of the gas-turbine system, such that the exhaust outlet is configured to provide exhaust gas to a heat recovery steam generator (HSRG). The manifold system may also include a control system that may adjust the one or more valves to couple the compressed air to the exhaust outlet when a temperature of the exhaust gas is above a threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presently disclosed systems and techniques will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 is a block diagram of an example combined cycle power plant that includes a heat recovery steam generator, in accordance with embodiments described herein;

FIG. 2 is a block diagram of a turbine system that employs an air extraction manifold system to adjust the temperature of exhaust gas provided to a heat recovery steam generator, in accordance with embodiments described herein; and

FIG. 3 is a flow chart of a method for controlling the temperature of exhaust gas provided to the heat recovery steam generator, in accordance with embodiments described herein.

DETAILED DESCRIPTION OF THE INVENTION

One or more specific embodiments of the presently disclosed systems and techniques will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the presently disclosed systems and techniques, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

The present disclosure is generally directed to systems and methods for controlling the inlet temperature of a heat recovery steam generator (HRSG). For example, a system may include a gas turbine that may be coupled to an HRSG, such that the exhaust gas from the gas turbine may be provided to the HRSG. Generally, the HRSG may use the heat from the exhaust gas to produce steam that may then be used to drive a steam turbine. As such, the HRSG enables the gas turbine to efficiently use the heat provided in exhaust gas to produce additional power.

The HRSG may be rated or designed to receive exhaust gas at or below a certain temperature. With this in mind, in one embodiment, a gas turbine system may employ a valve within a compressor of the gas turbine system to bleed compressed air from the compressor into an exhaust frame that may be provided to the HRSG. By bleeding the compressed air into the exhaust frame, the gas turbine system may decrease the temperature of the exhaust gas provided to the HRSG. As a result, the gas turbine system may ensure that the HRSG may operate at or below its rated temperature, thereby enabling the HRSG to operate efficiently and improve its operating lifespan. Additional details with regard to how the gas turbine system may control the temperature of the exhaust gas provided to the HRSG is provided below with reference to FIGS. 1-3.

By way of introduction, FIG. 1 is a block diagram of an embodiment of a combine cycle power plant 10 with a controller 12 that may control the temperature of the exhaust flow sent to a heat recovery steam generator. Moreover, the controller 12 may also enable the combined cycle power plant 10 to rapidly increase electrical output (i.e., loading) from an inactive state (i.e., no electrical output) to an active state (i.e., electrical output requested for grid), or in other words a starting load to a base load/dispatch power load. More specifically, the controller 12 may enable the combined cycle power plant 10 to increase power output from a gas turbine system 14 and a steam turbine system 16 through increased/accelerated steam production. In some embodiments, the increased/accelerated steam production may be used for a boiler, enabling a boiler to rapidly start.

Keeping this in mind, the combined cycle power plant (CCPP) 10 includes the controller 12, gas turbine system 14, the steam turbine system 16, and a heat recovery steam generator (HRSG) 18. In operation, the gas turbine system 14 combusts a fuel-air mixture to create torque that drives a load, e.g., an electrical generator. In order to reduce energy waste, the combined cycle power plant 10 uses the thermal energy in the exhaust gases to heat a fluid and create steam in the HRSG 18. The steam travels from the HRSG 18 through a steam turbine system 16 creating torque that drives a load, e.g., an electrical generator. Accordingly, the CCPP 10 combines the gas turbine system 14 with steam turbine system 16 to increase power production while reducing energy waste (e.g., thermal energy in the exhaust gas).

The gas turbine system 14 includes an airflow control module 20, compressor 22, combustor 24, and turbine 26. In operation, an oxidant 28 (e.g., air, oxygen, oxygen enriched air, or oxygen reduced air) enters the turbine system 14 through the airflow control module 20, which controls the amount of oxidant flow (e.g., airflow). The airflow control module 20 may control airflow by heating the oxidant flow, cooling the oxidant flow, extracting airflow from the compressor 22, using an inlet restriction, using an inlet guide vane, or a combination thereof. As the air passes through the airflow control module 20, the air enters the compressor 22. The compressor 22 pressurizes the air 28 in a series of compressor stages (e.g., rotor disks 30) with compressor blades. After the air 28 is pressurized, the pressurized air may reside in a compressor discharge chamber 29 before the compressed air exits the compressor 22.

As the compressed air exits the compressor 22, the air enters the combustor 24 and mixes with fuel 32. The turbine system 14 may use liquid or gas fuel, such as natural gas and/or a hydrogen rich synthetic gas, to run the turbine system 14. For example, the fuel nozzles 34 may inject a fuel-air mixture into the combustor 24 in a suitable ratio for optimal combustion, emissions, fuel consumption, and power output. As depicted, a plurality of fuel nozzles 34 intakes the fuel 32, mixes the fuel 32 with air, and distributes the air-fuel mixture into the combustor 24. The air-fuel mixture combusts in a combustion chamber within combustor 24, thereby creating hot pressurized exhaust gases. The combustor 24 directs the exhaust gases through a turbine 26 toward an exhaust outlet 36. As the exhaust gases pass through the turbine 26, the gases contact turbine blades attached to turbine rotor disks 38 (e.g., turbine stages). As the exhaust gases travel through the turbine 26, the exhaust gases may force turbine blades to rotate the rotor disks 38. The rotation of the rotor disks 38 induces rotation of shaft 40 and the rotor disks 32 in the compressor 26. A load 42 (e.g., electrical generator) connects to the shaft 40 and uses the rotation energy of the shaft 40 to generate electricity for use by the power grid.

As explained above, the combined cycle power plant 10 harvests energy from the hot exhaust gases exiting the gas turbine system 14 for use by the steam turbine system 16 or a boiler. Specifically, the CCPP 10 channels hot exhaust gases 44 from the turbine system 14 into the heat recovery steam generator (HRSG) 18. In the HRSG 18, the thermal energy in the combustion exhaust gases converts water into hot pressurized steam 46. The HRSG 18 releases the steam in line 46 for use in the steam turbine system 16.

The steam turbine system 16 includes a turbine 48, shaft 50, and load 52 (e.g., electrical generator). As the hot pressurized steam in line 46 enters the steam turbine 48, the steam contacts turbine blades attached to turbine rotor disks 54 (e.g., turbine stages). As the steam passes through the turbine stages in the turbine 48, the steam induces the turbine blades to rotate the rotor disks 54. The rotation of the rotor disks 54 induces rotation of the shaft 50. As illustrated, the load 52 (e.g., electrical generator) connects to the shaft 50. Accordingly, as the shaft 50 rotates, the load 52 (e.g., electrical generator) uses the rotation energy to generate electricity for the power grid. As the pressurized steam in line 46 passes through the turbine 48, the steam loses energy (i.e., expands and cools). After exiting the steam turbine 48, the steam enters a condenser 49 before being routed back to the HRSG 18, where the steam is reheated for reuse in the steam turbine system 16.

As explained above, the controller 12 enables the combined cycle power plant 10 to flexibly load the gas turbine system 14, which may enable increased steam production in the HRSG 18. The controller 12 may also be employed to control the temperature of the exhaust gas provided to the HRSG 18. As mentioned above, the HRSG 18 may be associated with a temperature rating or threshold that described its preferred operating temperature. In some cases, the threshold may be associated with an upper limit (e.g., 10%) of the operating range of the HSRG 18 to enable the controller 12 to react and change the operation of the CCPP 10. If the controller 12 detects that the exhaust temperature provided to the HRSG 18 is above this threshold, the controller 12 may decrease the firing temperature of the air-fuel mixture combusted in the combustor 24 to ensure that the HRSG 18 operates efficiently. However, in decreasing the firing temperature, the controller 12 may decrease the operating efficiency of the CCPP 10.

With this in mind, in one embodiment, the controller 12 may monitor the temperature of the exhaust gas provided to the HRSG 18 and bleed off compressed air from the compressor discharge chamber 29, such that the temperature of the resulting exhaust/air mixture within the exhaust outlet 36 is reduced. As a result, the combustor 24 may maintain its firing temperature while the controller 12 ensures that the HRSG 18 operates at a desired temperature range. Additional details regarding how the controller 12 may adjust the temperature of the exhaust gas will be described below with reference to FIGS. 2 and 3.

Generally, the controller 12 may include a memory 56 and a processor 58. The memory 56 stores instructions and steps written in software code. The processor 58 executes the stored instructions in response to feedback from the CCPP 10. More specifically, the controller 12 controls and communicates with various components in the CCPP 10 in order to flexibly control the loading of the gas turbine system 14, and thus the loading of the steam turbine system 16. As illustrated, the controller 12 controls the airflow control module 20, the intake of fuel 32, and valve(s) 47; and communicates with load 42, exhaust gas temperature sensor 60, HRSG steam temperature sensor 62, and steam turbine metal temperature sensor 64, in order to load the CCPP 10 along different load paths.

In operation, the controller 12 controls the airflow control module 20 and the consumption of fuel 32 to change the loading of the gas turbine system 14 and thereby the loading of CCPP 10 (i.e., how the CCPP 10 increases electrical power output to the grid). Specifically, the controller 12 adjusts the mass flow rate and temperature of the exhaust gas 44, which controls how rapidly the HRSG 18 produces steam for the steam turbine system 16, and therefore, how quickly the CCPP 10 produces electrical power using loads 42 and 52. For example, when the controller 12 increases the airflow with the airflow control module 20, it increases the amount of airflow flowing through the compressor 22, flow through the combustor 24, and flow through the turbine 26. The increase in airflow increases the mass flow rate of the exhaust gas, and thus the torque of the shaft 40. Moreover, the increase in the mass flow rate of the exhaust gas 44 increases the amount of thermal energy available for the HRSG 18 to produce steam (i.e., more exhaust gas is flowing through the HRSG 18). An increase in steam production by the HRSG 18 reduces startup time for the steam turbine system 16 and thus increases electrical output from the load 52.

As explained above, the controller 12 controls fuel consumption by the gas turbine system 14. Control of the fuel 32 affects the mass flow rate through the gas turbine system 14 and the thermal energy available for the HRSG 18. For example, when the controller 12 increases fuel consumption the temperature of the exhaust gas 44 increases. The increase in the exhaust gas temperature 44 enables the HRSG 18 to produce steam at higher temperatures and pressures, which translates into more power production by the steam turbine system 16. However, when the controller 12 decreases fuel consumption there is a reduction in the temperature of the exhaust gas. Accordingly, there is less mechanical energy available to drive load 42 and less thermal energy available to produce steam for the steam turbine system 16 to drive load 52.

Although the controller 12 has been described as having the memory 56 and the processor 58, it should be noted that the controller 12 may include a number of other computer system components to enable the controller 12 to control the operations of the CCPP 10 and the related components. For example, the controller 12 may include a communication component that enables the controller 12 to communicate with other computing systems. The controller 12 may also include an input/output component that enables the controller 12 to interface with users via a graphical user interface or the like.

FIG. 2 is a block diagram of an air extraction system 70 for controlling the temperature of exhaust gas provided to the HRSG 18. As illustrated in FIG. 2, the air extraction system 70 may include an air extraction manifold system 72 coupled to the compressor discharge chamber 29 via piping 74. In one embodiment, the piping 74 may be a 10-inch expansion joint that couples the compressor discharge chamber 29 to the air extraction manifold system 72.

The air extraction manifold system 72 may include a chamber of one or more valves that may direct air or gases received by the air extraction manifold system 72 to various destinations. For example, the air extraction manifold system 72 may be coupled to an inlet bleed heat system and to the exhaust outlet 36 (e.g., overboard bleed system). As such, the air extraction manifold system 72 may direct the compressed air from the compressor discharge chamber 29 to the inlet bleed heat system, the exhaust outlet 36, or a variety of proportions between the two.

In one embodiment, the air extraction manifold system 72 may include a control system that is capable of controlling the valves within the air extraction manifold system 72. Moreover, the control system may be capable of sending and receiving data similar to the functions described herein with regard to the controller 12.

The inlet bleed heat system may reduce the flow of air through the combustor 24 by recirculating a portion of the compressed air via the compressor discharge chamber 29 to an inlet air duct that is coupled to the compressor 22. As such, the compressed air may heat inlet air provided to the compressor 22, thereby making the inlet air less dense and increasing the operating range of the compressor 22.

In one embodiment, the air extraction manifold system 72 may direct the compressed air from the compressor discharge chamber 29 to the exhaust outlet 36, thereby adding a certain amount of compressed air that has not been through the combustor 24 to the exhaust gas output via the turbine 26. As a result, the compressed air may cool or lower the overall temperature of the exhaust gas present in the exhaust outlet 36. In this way, the gas provided to the HRSG 18 may have a lower temperature, as compared to receiving the exhaust gas without the added compressed air via the air extraction manifold system 72.

To control when the compressed air will be provided to the exhaust outlet 36, the controller 12 may monitor the temperature of the exhaust gas in the exhaust outlet 36, determine whether the temperature is greater than a threshold, and send a command to the air extraction manifold system 72 to direct compressed air to the exhaust outlet 36 when the temperature is greater than the threshold. As a result, the temperature of the exhaust gas provided to the HSRG 18 may start to decrease.

By way of example, FIG. 3 illustrates a flow chart of a method 90 employed by the controller 12 to control the temperature of the gas within the exhaust outlet 36. Although the following description of the method 90 will be described as being performed by the controller 12, it should be noted that the method 90 may be performed by any suitable computing device including a computing device that is remotely positioned with respect to the CCIP 10.

Referring now to FIG. 3, at block 92, the controller 12 may monitor the temperature of the exhaust gas mixture within the exhaust outlet 36. In one embodiment, the controller 12 may model the temperature of the exhaust gas mixture in the exhaust outlet based on a mixing mass flow of the compressed air via the piping 74, the mass flow of the exhaust gas in the exhaust outlet 36, the temperature of the compressed air in the piping 74, and the temperature of the exhaust gas in the exhaust outlet 36. In one embodiment, the mass flow of the compressed air in the piping 74 may be determined based on known gas turbine system parameters, such as a differential pressure sensor associated with the piping 74 and fluid mechanics. Moreover, the mass flow of the exhaust gas, as well as the temperature of the compressed air and the exhaust gas may be modeled based on known baseline parameters regarding the air 28, the compressor 22, the combustor 24, the fuel 32, the turbine 26, and the like. Using the data described above, the controller 12 may model an expected temperature of the exhaust gas mixture present in the exhaust outlet 36.

In some embodiments, the piping 74 and the exhaust outlet 36 may each include a temperature sensor (e.g., thermocouple) that may indicate the respective temperatures of the compressed air in the piping 74 and the exhaust gas in the exhaust outlet 36. As such, the controller 12 may use the temperature data from the temperature sensors to determine the temperature of the exhaust gas mixture in the exhaust outlet 36.

After receiving the expected temperature associated with the exhaust outlet 36, at block 94, the controller 12 may determine whether the expected temperature is greater than a threshold. The threshold may be defined by the user or automatically determined based on the operating parameters (e.g., operating temperature range) associated with the HRSG 18. As mentioned above, the threshold may be related to an upper limit (e.g., 10%) of the operating range of the HSRG 18. As such, the controller 12 may have a sufficient amount of time to divert the compressed air to the exhaust outlet 36 before the temperature of the exhaust gas provided to the HSRG 18 exceeds the operating range of the HSRG 18.

If the temperature is not greater than the threshold, the controller 12 may return to block 92 and continue monitoring the temperature of the exhaust gas in the exhaust outlet 36. If, however, the temperature is greater than the threshold, the controller 12 may proceed to block 96.

At block 96, the controller 12 may send a command to the air extraction manifold system 72 to open one or more valves within the air extraction manifold system 72 to provide a portion of the compressed air within the compressor discharge chamber 29 to the exhaust outlet 36 via the piping 74. In one embodiment, the controller 12 may specify a valve setting in order to bleed a sufficient amount of compressed air to the exhaust outlet 36 based on a difference between the monitored temperature of the exhaust outlet 36 and the threshold.

After sending the command to provide compressed air to the exhaust outlet 36, the controller 12 may return to block 92 and monitor the new temperature of the exhaust gas in the exhaust outlet 36 based on the provided compressed air. The controller 12 may then perform the method 90 continuously until the temperature of the exhaust outlet 36 is at or below the threshold.

Technical effects of the presently disclosed systems and techniques include improving the operating efficiency of the HSRG 18 by adjusting the temperature of the exhaust gas provided to the HSRG 18. Moreover, by preventing exhaust gas that is above a temperature threshold from being input into the HSRG 18, the controller 12 may prevent overloading the CCPP 10, powering down the CCPP 10, or the like.

In addition, by controlling the temperature of the exhaust gas provided to the HSRG 18, the controller 12 may provide an enhanced turn down mode for the operation of the CCPP 10. That is, the CCPP 10 may continue to operate by providing power to loads during off-peak hours, which may involve producing exhaust gas having temperatures above the threshold. However, by diverting the compressed air to the exhaust outlet 36 during off-peak hours, the CCPP 10 may continue to provide power to the loads even with the high exhaust temperatures by using the compressed air to cool the high exhaust temperatures.

This written description uses examples to disclose various embodiments of the presently disclosed systems and techniques, including the best mode, and to enable any person skilled in the art to practice the embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the presently disclosed systems and techniques is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

1. A system comprising: a gas turbine system comprising a compressor, wherein the gas turbine system is configured to produce exhaust gas in an exhaust outlet when generating electricity; a heat recovery steam generator (HRSG) configured to use the exhaust gas to create steam; a manifold system configured to couple compressed air in the compressor to the exhaust outlet; and a controller configured to send a command to the manifold system to couple the compressed air to the exhaust outlet when a temperature of the exhaust gas is above a threshold.
 2. The system of claim 1, comprising a steam turbine system configured to receive the steam.
 3. The system of claim 1, wherein the controller is configured to model the temperature of the exhaust gas based on a mass flow of the compressed air, a mass flow of the exhaust gas, a temperature of the compressed air, a temperature of the exhaust gas, or any combination thereof.
 4. The system of claim 3, wherein the mass flow of the compressed air is determined based on a pressure sensor measurement received via a differential pressure sensor associated with the compressed air.
 5. The system of claim 3, wherein the mass flow of the exhaust gas is determined based on known gas turbine system parameters.
 6. The system of claim 1, wherein the temperature of the compressed air or the temperature of the exhaust gas is acquired via a temperature sensor.
 7. The system of claim 1, wherein the compressor comprises a compressor discharge chamber, wherein the compressed air is coupled to the exhaust outlet via the compressor discharge chamber .
 8. The system of claim 1, wherein the manifold system comprises one or more valves configured to direct at least a portion of the compressed air to the exhaust outlet.
 9. The system of claim 1, wherein the threshold is associated with an operating range of the HSRG.
 10. A non-transitory machine readable medium, comprising computer-executable instructions configured to cause a processor to: monitor a temperature of exhaust gas provided to a heat recovery steam generator (HSRG) via an exhaust outlet; and send a command to a manifold system when the temperature exceeds a threshold, wherein the command is configured to cause the manifold system to couple compressed air to the exhaust outlet.
 11. The non-transitory machine readable medium of claim 10, wherein the computer-executable instructions to cause the processor to monitor the temperature comprises instructions to cause the processor to receive the temperature via a temperature sensor associated with the exhaust outlet.
 12. The non-transitory machine readable medium of claim 10, wherein the computer-executable instructions to cause the processor to monitor the temperature comprises instructions to cause the processor to model the temperature of the exhaust outlet based on a mass flow of the compressed air, a mass flow of the exhaust gas, a temperature of the compressed air, a temperature of the exhaust gas, or any combination thereof.
 13. The non-transitory machine readable medium of claim 12, wherein the mass flow of the compressed air is determined based on a pressure sensor measurement received via a differential pressure sensor associated with the compressed air.
 14. The non-transitory machine readable medium of claim 12, wherein the mass flow of the exhaust gas is determined based on known gas turbine system parameters.
 15. The non-transitory machine readable medium of claim 10, wherein the threshold is associated with an operating range of the HSRG.
 16. A manifold system, comprising: one or more valves configured to couple compressed air from a compressor of a gas-turbine system to an exhaust outlet of the gas-turbine system, wherein the exhaust outlet is configured to provide exhaust gas to a heat recovery steam generator (HSRG); and a control system configured to adjust the one or more valves to couple the compressed air to the exhaust outlet when a temperature of the exhaust gas is above a threshold.
 17. The manifold system of claim 16, wherein at least one of the one or more valves is coupled to a compressor discharge chamber of the compressor.
 18. The manifold system of claim 16, wherein at least one of the one or more valves is coupled to an inlet bleed heat system associated with the gas-turbine system.
 19. The manifold system of claim 16, wherein the threshold is associated with an operating range of the HSRG.
 20. The manifold system of claim 16, wherein the control system is configured to adjust the one or more valves to decouple the compressed air from the exhaust outlet after the temperature of the exhaust gas returns to below the threshold. 